Nitride crystal, nitride crystal substrate, epilayer-containing nitride crystal substrate, semiconductor device and method of manufacturing the same

ABSTRACT

A nitride crystal is characterized in that, in connection with plane spacing of arbitrary specific parallel crystal lattice planes of the nitride crystal obtained from X-ray diffraction measurement performed with variation of X-ray penetration depth from a surface of the crystal while X-ray diffraction conditions of the specific parallel crystal lattice planes are satisfied, a uniform distortion at a surface layer of the crystal represented by a value of |d 1 −d 2 |/d 2  obtained from the plane spacing d 1  at the X-ray penetration depth of 0.3 μm and the plane spacing d 2  at the X-ray penetration depth of 5 μm is equal to or lower than 2.1×10 −3 . The above configuration provides the nitride crystal having a crystal surface layer that is evaluated directly and reliably without breaking the crystal so that it can be used in a preferred fashion as a substrate for a semiconductor device as well as the nitride crystal substrate, an epilayer-containing nitride crystal substrate, a semiconductor device and a method of manufacturing the same.

RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.11/473,122, filed Jun. 23, 2006, claiming priority of JapaneseApplication No. 2005-183111, filed Jun. 23, 2005, the entire contents ofeach of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nitride crystal, a nitride crystalsubstrate, an epilayer-containing nitride crystal substrate, asemiconductor device and a method of manufacturing the same, andparticularly to a nitride crystal that can be preferably used as asubstrate for growing an epitaxial crystal when producing asemiconductor device.

2. Description of the Background Art

As is well known, various devices using nitride semiconductor crystalshave been produced in recent years, and nitride semiconductor lightemitting devices have been produced as a typical example of suchsemiconductor devices.

Generally, in a process of manufacturing a nitride semiconductor device,a plurality of nitride semiconductor layers are epitaxially grown on asubstrate. Crystal quality of the epitaxially grown nitridesemiconductor layer is affected by a state of a surface layer of thesubstrate used for the epitaxial growth, and this quality affectsperformance of the semiconductor device including the nitridesemiconductor layer. Therefore, in the case where the nitridesemiconductor crystal is used as the above kind of substrate, it isdesired that at least a main surface of the substrate providing a baseof epitaxial growth has a smooth form without a distortion.

More specifically, the main surface of the nitride semiconductorsubstrate used for the epitaxial growth is generally subjected tosmoothing processing and distortion removal processing. Among variouscompound semiconductors, gallium-nitride-based semiconductors arerelatively hard so that the surface smoothing processing thereof is noteasy, and the distortion removal processing after the smoothingprocessing is not easy.

Japanese Patent Laying-Open No. 2004-311575 has disclosed a polishingmethod that uses soft grains and hard grains as polishing compounds forpolishing a surface of a nitride gallium substrate. U.S. Pat. No.6,596,079 has disclosed a method of forming a substrate surface in thecase where the substrate is produced from an (AlGaIn)N bulk crystalgrown by vapor phase epitaxy on an (AlGaIn)N seed crystal, and morespecifically a method of forming a substrate surface that has a RMS(Root Mean Square) surface roughness of 1 nm or lower, and does not havea surface damage owing to effecting CMP (Chemical-Mechanical Polishing)or etching on the substrate surface subjected to mechanical polishing.U.S. Pat. No. 6,488,767 has disclosed an Al_(x)Ga_(y)In_(z)N (0<y≦1,x+y+z=1) substrate having an RMS surface roughness of 0.15 nm attainedby the CMP processing. A processing agent for this CMP contains Al₂O₃grains, SiO₂ grains, pH controlling agent and oxidizer. According toJapanese Patent Laying-Open No. 2001-322899, a work-affected layer isremoved by dry etching to finish the substrate surface after polishingthe GaN substrate.

In the prior art, as described above, the CMP processing or dry etchingis effected after mechanically polishing the GaN crystal so that thework-affected layer formed by the mechanical polishing is removed, andthe GaN substrate having the finished substrate surface is formed.However, the processing rate of the CMP processing is low, and causesproblems in cost and productivity. Further, the dry etching causes aproblem in surface roughness.

The finishing method of the Si substrate using the CMP as well as thepolishing agent for the method are not suitable for the hard nitridesemiconductor substrate, and lower the removal speed of the surfacelayer. In particular, GaN is chemically suitable, and is relativelyresistant to the wet etching so that the CMP processing is not easy.Although the dry etching can remove the nitride semiconductor surface,it does not have an effect of flattening the surface in a horizontaldirection so that the surface smoothing effect cannot be achieved.

For epitaxially growing the compound semiconductor layer of good crystalquality on the substrate surface, it is necessary to use the substratesurface having good crystal quality as well as less work damage and lessdistortion as described above. However, the crystal quality of thesurface layer that is required at the substrate surface is not clear.

In the prior art, distortions at the surface layer of the crystal areevaluated by cleaving the crystal, and observing the cleavage plane witha TEM (Transmission Electron Microscope) as disclosed, e.g., in S. S.Park et al, “Free-Standing GaN Substrate by Hydride Vapor PhaseEpitaxy”, Jpn, J. Appl. Phys., The Japan Society of Applied Physics,Vol. 39, November 2000, pp. Li 141-L1142 and Yutaka TAKAHASHI et al,“Transmission Electron Microscopy of Surface Damages Resulting from WetPolishing in a Polycrystalline Aluminum Nitride Substrate”, The AcademicJournal of the Ceramic Society of Japan, The Ceramic Society of Japan,99, [7], (1991), pp. 613-619. Thus, the distortions at the surface layerof the crystal have conventionally been evaluated by a breaking testthat breaks the crystal, and therefore such problems occur thatcorrection cannot be performed after the evaluation even when the resultof evaluation was insufficient, and that the evaluation cannot beeffected on the product in itself. Under the present circumstances,there is no index for nondestructively evaluating the crystallinity ofthe surface layer at the finished substrate surface, and it is difficultto define quantitatively the crystal quality of the surface layer.

SUMMARY OF THE INVENTION

An object of the invention is to provide a nitride crystal, a nitridecrystal substrate having a crystal surface layer that is evaluateddirectly and reliably without breaking the crystal so that it can beused in a preferred fashion as a substrate for epitaxial crystal growthwhen producing a semiconductor device, as well as an epilayer-containingnitride crystal substrate, a semiconductor device and a method ofmanufacturing the same.

According to an aspect of the invention, a nitride crystal ischaracterized in that, in connection with plane spacing of arbitraryspecific parallel crystal lattice planes of the nitride crystal obtainedfrom X-ray diffraction measurement performed with variation of X-raypenetration depth from a surface of the crystal while X-ray diffractionconditions of the specific parallel crystal lattice planes aresatisfied, a uniform distortion at a surface layer of the crystalrepresented by a value of |d₁−d₂|/d₂ obtained from the plane spacing d₁at the X-ray penetration depth of 0.3 μm and the plane spacing d₂ at theX-ray penetration depth of 5 μm is equal to or lower than 2.1×10⁻³.

According to another aspect of the invention, a nitride crystal ischaracterized in that, on a diffraction intensity profile of arbitraryspecific parallel crystal lattice planes of the nitride crystal obtainedfrom X-ray diffraction measurement performed with variation of X-raypenetration depth from a surface of the crystal while X-ray diffractionconditions of the specific parallel crystal lattice planes aresatisfied, an irregular distortion at a surface layer of the crystalrepresented by a value of |v₁−v₂| obtained from a half value width v₁ ofa diffraction intensity peak at the X-ray penetration depth of 0.3 μmand a half value width v₂ of the diffraction intensity peak at the X-raypenetration depth of 5 μm is equal to or lower than 150 arcsec.

According to still another aspect of the invention, a nitride crystal ischaracterized in that, on a rocking curve measured by varying an X-raypenetration depth from a crystal surface in connection with X-raydiffraction of arbitrary specific parallel crystal lattice planes of thenitride crystal, a plane orientation deviation of the specific parallelcrystal lattice planes represented by a value of |w₁−w₂| obtained from ahalf value width w₁ of a diffraction intensity peak at the X-raypenetration depth of 0.3 μm and a half value width w₂ of the diffractionintensity peak at the X-ray penetration depth of 5 μm is equal to orlower than 400 arcsec.

Preferably, the surface of the nitride crystal has a surface roughnessRy of 30 nm or lower. It is also preferable that the surface of thenitride crystal has the surface roughness Ry of 3 nm or lower.

Preferably, the surface of the nitride crystal is parallel to a C-planeof a wurtzite structure. It is also preferable that the surface of thenitride crystal has an off angle in a range from 0.05° to 15° withrespect to a C-plane of a wurtzite structure.

A nitride crystal substrate formed of the nitride crystal describedabove is preferable as a substrate for a semiconductor device. Anepilayer-containing nitride crystal substrate including one or moresemiconductor layer(s) formed by epitaxial growth on at least one ofmain surface sides of the nitride crystal substrate is also preferableas the substrate for the semiconductor device. The epilayer is one ormore semiconductor layer(s) formed by epitaxial growth on at least oneof the main surface sides of the nitride crystal substrate.

According to still another aspect of the invention, a semiconductordevice is a semiconductor device including the nitride crystal substrateor the epilayer-containing nitride crystal substrate described above asthe substrate. The semiconductor device of this aspect includes one ormore semiconductor layer(s) formed by epitaxial growth on at least oneof the main surface sides of the substrate.

According to a yet another aspect of the invention, a semiconductordevice is a semiconductor device including the nitride crystal substrateor the epilayer-containing nitride crystal substrate described above asthe substrate. The semiconductor device of this aspect includes alight-emitting element including three or more semiconductor layersformed by epitaxial growth on one of the main surface sides of thesubstrate, a first electrode formed on the other main surface side ofthe nitride crystal substrate or the epilayer-containing nitride crystalsubstrate, and a second electrode formed on the outermost semiconductorlayer among the plurality of semiconductor layers, and further includesa conductor bearing the light-emitting element. Further, thesemiconductor device of this aspect is configured such that a side ofthe substrate of the light emitting element is has a light emitting sideand the outermost semiconductor layer side is a mount side, and theplurality of semiconductor layers include a p-type semiconductor layer,an n-type semiconductor layer and a light emitting layer formed betweenthese conductive semiconductor layers.

According to a further aspect of the invention, a method ofmanufacturing a semiconductor device is a method of manufacturing asemiconductor device including, as a substrate, a nitride crystalsubstrate or an epilayer-containing nitride crystal substrate includingone or more semiconductor layer(s) formed by epitaxial growth on atleast one of main surface sides of the nitride crystal substrate. Themethod selects, as the nitride crystal substrate, nitride crystalconfigured such that, in connection with plane spacing of arbitraryspecific parallel crystal lattice planes of the crystal obtained fromX-ray diffraction measurement performed with variation of X-raypenetration depth from a surface of the crystal while X-ray diffractionconditions of the specific parallel crystal lattice planes aresatisfied, a uniform distortion at a surface layer of the crystalrepresented by a value of |d₁−d₂|/d₂ obtained from the plane spacing d₁at the X-ray penetration depth of 0.3 μm and the plane spacing d₂ at theX-ray penetration depth of 5 μm is equal to or lower than 2.1×10⁻³.Further, the method of manufacturing the semiconductor of this aspectincludes a step of epitaxially growing one or more semiconductorlayer(s) on at least one of main surface sides of the substrate.

According to a further aspect of the invention, a method ofmanufacturing a semiconductor device is a method of manufacturing asemiconductor device including, as a substrate, a nitride crystalsubstrate or an epilayer-containing nitride crystal substrate includingone or more semiconductor layer(s) formed by epitaxial growth on atleast one of main surface sides of the nitride crystal substrate. Themethod selects, as the nitride crystal substrate, nitride crystalconfigured such that, on a diffraction intensity profile of arbitraryspecific parallel crystal lattice planes of the nitride crystal obtainedfrom X-ray diffraction measurement performed with variation of X-raypenetration depth from a surface of the crystal while X-ray diffractionconditions of the specific parallel crystal lattice planes aresatisfied, an irregular distortion at a surface layer of the crystalrepresented by a value of |v₁−v₂| obtained from a half value width v₁ ofa diffraction intensity peak at the X-ray penetration depth of 0.3 μmand a half value width v₂ of the diffraction intensity peak at the X-raypenetration depth of 5 μm is equal to or lower than 150 arcsec. Further,the method of manufacturing the semiconductor of this aspect includes astep of epitaxially growing one or more semiconductor layer(s) on atleast one of main surface sides of the substrate.

According to a further aspect of the invention, a method ofmanufacturing a semiconductor device is a method of manufacturing asemiconductor device including, as a substrate, a nitride crystalsubstrate or an epilayer-containing nitride crystal substrate includingone or more semiconductor layer(s) formed by epitaxial growth on atleast one of main surface sides of the nitride crystal substrate. Themethod selects, as the nitride crystal substrate, nitride crystalconfigured such that, on a rocking curve measured by varying an X-raypenetration depth from a crystal surface in connection with X-raydiffraction of arbitrary specific parallel crystal lattice planes of thenitride crystal, a plane orientation deviation of the specific parallelcrystal lattice planes represented by a value of |w₁−w₂| obtained from ahalf value width w₁ of a diffraction intensity peak at the X-raypenetration depth of 0.3 μm and a half value width w₂ of the diffractionintensity peak at the X-ray penetration depth of 5 μm is equal to orlower than 400 arcsec. Further, the method of manufacturing thesemiconductor of this aspect includes a step of epitaxially growing oneor more semiconductor layer(s) on at least one of main surface sides ofthe substrate.

The invention can provide the nitride crystal having a crystal surfacelayer that is evaluated directly and reliably without breaking thecrystal so that it can be used in a preferred fashion as a substrate forepitaxial crystal growth when producing a semiconductor device as wellas the nitride crystal substrate, the epilayer-containing nitridecrystal substrate, the semiconductor device and the method ofmanufacturing the same.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic section showing a state of a crystal in a depthdirection from a crystal surface.

FIG. 2 is a schematic view showing measurement axes and measurementangles in an X-ray diffraction method according to the invention.

FIG. 3 schematically illustrates a relationship between a uniformdistortion of a crystal lattice of a nitride crystal and plane spacingof specific parallel crystal lattice planes is shown on a diffractionprofile in the X-ray diffraction method. At (a), the uniform distortionof the crystal lattice is illustrated. At (b), the plane spacing of thespecific parallel crystal lattice plane is shown on the diffractionprofile.

FIG. 4 schematically illustrates a relationship between irregulardistortion of a crystal lattice of a nitride crystal and a half valuewidth of a diffraction peak on a diffraction profile in the X-raydiffraction method. At (a), the irregular distortion of the crystallattice is illustrated. At (b), the half value width of the diffractionpeak on the diffraction profile is illustrated.

FIG. 5 schematically illustrates a relationship between planeorientation distortion of specific parallel crystal lattice planes of anitride crystal and a half value width on a rocking curve in the X-raydiffraction method. At (a), the plane orientation deviation of thespecific parallel crystal lattice planes is illustrated. At (b), thehalf value width of the diffraction peak on the rocking curve isillustrated.

FIG. 6 is a schematic section showing an example of a semiconductordevice according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention employs an X-ray diffraction method, and thereby canperform direct evaluation of crystallinity at a surface layer of anitride crystal without breaking the crystal. The evaluation of thecrystallinity represents evaluation or determination of an extent ordegree to which a distortion of the crystal is present, and morespecifically represents evaluation of an extent or degree to which adistortion of a crystal lattice and a plane orientation deviation of thelattice plane are present. The distortion of the crystal lattice can bespecifically classified into a uniform distortion caused by a uniformlydistorted crystal lattice and an irregular distortion caused by anirregularly distorted crystal lattice. The plane orientation deviationof the crystal lattice planes represent a magnitude by which the planeorientation of the lattice plane of each crystal region deviates from anaverage orientation of the plane orientation of the lattice planes ofthe whole crystal lattice.

As shown in FIG. 1, a nitride crystal 1 has a crystal surface layer 1 ahaving a certain depth from a crystal surface 1 s, and this crystalsurface layer 1 a has a uniform distortion, an irregular distortionand/or a plane orientation deviation of a crystal lattice occur incrystal surface layer 1 a due to working such as cutting, grinding orpolishing. The uniform distortion, irregular distortion and/or planeorientation deviation of the crystal lattice may occur in asurface-neighboring layer 1 b neighboring to crystal surface layer 1 a(FIG. 1 shows a case where the plane orientation deviation of thecrystal lattice is present. Further, it can be considered that a crystalinner layer 1 c located inside surface-neighboring layer 1 b has anoriginal crystal structure of the crystal. The states and thicknesses ofcrystal surface layer 1 a and surface-neighboring layer 1 b depend onthe manner and extent of the grinding or polishing in the surfaceworking processing.

In the above structure, the uniform distortion, irregular distortionand/or plane direction deviation of the crystal lattice are evaluated inthe depth direction from the surface of the crystal so that thecrystallinity of the crystal surface layer can be directly and reliablyevaluated.

In the X-ray diffraction measurement for evaluating the crystallinity ofthe surface layer of the nitride crystal according to the invention, anX-ray penetration depth from the surface of the crystal is changed whileX-ray diffraction conditions of arbitrary specific parallel crystallattice planes of the nitride crystal are satisfied.

The diffraction conditions of the arbitrary specific parallel crystallattice planes represent conditions under which the arbitrarilyspecified parallel crystal lattice planes diffracts the X-ray. Assumingthat a Bragg angle is θ, a wavelength of the X-ray is λ and a planespacing of the crystal lattice planes is d, the X-ray is diffracted bythe crystal lattice plane satisfying the Bragg's condition (2 dsinθ=nλ,where n is an integer).

The X-ray penetration depth represents a distance that is measured inthe depth direction perpendicular to crystal surface 1 s, and causes anintensity of the incident X-ray equal to 1/e where e is a base of thenatural logarithm. Referring to FIG. 2, an X-ray linear absorptioncoefficient μ of crystal 1, an inclination angle λ of crystal surface 1s, an X-ray incident angle ω with respect to crystal surface 1 s and aBragg angle θ in crystal surface 1 s determines X-ray penetration depthT that is expressed by an equation (1). A φ represents a rotation anglein crystal surface. A X axis 21 is present on a plane formed by anincident X-ray 11 and an outgoing X-ray 12, a ω axis (2θ axis) 22 isperpendicular to a plane formed by incident X-ray 11 and outgoing X-ray12, and a φ axis 23 is perpendicular to crystal surface 1 s.

$\begin{matrix}{T = {\frac{1}{\mu} \cdot \frac{\cos \; {\chi \cdot \sin}\; {\omega \cdot {\sin \left( {{2\; \theta} - \omega} \right)}}}{{\sin \; \omega} + {\sin \; \left( {{2\; \theta} - \omega} \right)}}}} & (1)\end{matrix}$

Therefore, X-ray penetration depth T can be continuously changed byadjusting at least one of X, ω and φ to satisfy the diffractionconditions for the above specific crystal lattice planes.

For continuously changing X-ray penetration depth T to satisfy thediffraction conditions for a specific crystal lattice plane 1 d, it isnecessary that specific crystal lattice plane 1 d is not parallel tocrystal surface 1 s. If specific crystal lattice plane 1 d is parallelto crystal surface 1 s, the angle θ between crystal lattice plane 1 dand incident X-ray 11 becomes equal to angle ω between crystal surface 1s and incident X-ray 11 so that the X-ray penetration depth cannot bechanged at specific crystal lattice plane 1 d.

Based on the following embodiment, description will now be given on theevaluation performed in such a manner that the arbitrary specificparallel crystal lattice planes of the crystal is irradiated with theX-ray while changing the X-ray penetration depth, the uniform distortionof the crystal lattice is evaluated from the change in plane spacing onthe diffraction profile relating to this specific parallel crystallattice planes, the irregular distortion of the crystal lattice isevaluated from the change in half value width of the diffraction peak onthe diffraction profile and the plane orientation deviation of thecrystal lattice is evaluated from the change in half value width on therocking curve.

First Embodiment

A nitride crystal of this embodiment is characterized in that, inconnection with plane spacing of arbitrary specific parallel crystallattice planes of the crystal obtained from X-ray diffractionmeasurement performed with variation of X-ray penetration depth from asurface of the crystal while X-ray diffraction conditions of thespecific parallel crystal lattice planes are satisfied, a uniformdistortion at a surface layer of the crystal represented by a value of|d₁−d₂|/d₂ obtained from a plane spacing d₁ at the X-ray penetrationdepth of 0.3 μm and a plane spacing d₂ at the X-ray penetration depth of5 μm is equal to or lower than 2.1×10⁻³.

Referring to FIG. 1, the X-ray penetration depth of 0.3 μm correspondsto a distance from the surface of the nitride crystal to an inside ofcrystal surface layer 1 a, and the X-ray penetration depth of 5 μmcorresponds to a distance from the surface of the nitride crystal to aninside of crystal inner layer 1 c. Referring to FIG. 3( a), planespacing d₂ at the X-ray penetration depth of 5 μm can be considered asthe plane spacing of the specific parallel crystal lattice planes of thenitride crystal in the original state, but plane spacing d₁ at the X-raypenetration depth of 0.3 μm reflects the uniform distortion of thecrystal lattice at the crystal surface layer due to an influence (e.g.,a tensile stress 30 toward an inside of the crystal lattice plane) ofsurface working of the crystal, and therefore takes a value differentfrom plane spacing d₂ at the X-ray penetration depth of 5 μm.

Referring to FIG. 3( b), plane spacing d₁ at the X-ray penetration depthof 0.3 μm and plane spacing d₂ at the X-ray penetration depth of 5 μmappear on the diffraction profile relating to the arbitrary specificparallel crystal lattice planes of the crystal in the above case.Therefore, the uniform distortion of the crystal surface layer can beexpressed by the value of a ratio |d₁−d₂|/d₂ of a difference between d₁and d₂ with respect to d₂.

In the nitride crystal of this embodiment, the uniform distortion at thesurface layer represented by |d₁−d₂|/d₂ is equal to or lower than2.1×10⁻³. Owing to the fact that the uniform distortion at the surfacelayer of the nitride crystal satisfies the relationship of|d₁−d₂|/d₂≦2.1×10⁻³, a semiconductor layer of good crystallinity can beepitaxially grown on the nitride crystal, and a semiconductor device ofgood characteristics can be produced.

Second Embodiment

A nitride crystal of this embodiment is characterized in that, on adiffraction intensity profile of arbitrary specific parallel crystallattice planes of the crystal obtained from X-ray diffractionmeasurement performed with variation of X-ray penetration depth from asurface of the crystal while X-ray diffraction conditions of thespecific parallel crystal lattice planes are satisfied, an irregulardistortion at a surface layer of the crystal represented by a value of|v₁−v₂| obtained from a half value width v₁ of a diffraction intensitypeak at the X-ray penetration depth of 0.3 μm and a half value width v₂of the diffraction intensity peak at the X-ray penetration depth of 5 μmis equal to or lower than 150 arcsec.

Referring to FIG. 1, the X-ray penetration depth of 0.3 μm correspondsto a distance from the surface of the nitride crystal to an inside ofcrystal surface layer 1 a, and the X-ray penetration depth of 5 μmcorresponds to a distance from the surface of the nitride crystal to aninside of crystal inner layer 1 c. Referring to FIG. 4( a), half valuewidth v₂ of the diffraction peak at the X-ray penetration depth of 5 μmcan be considered as the half value width of the nitride crystal in theoriginal state, but half value width v₁ of the diffraction peak at theX-ray penetration depth of 0.3 μm reflects the irregular distortion ofthe crystal lattice at the crystal surface layer due to an influence ofsurface working of the crystal (e.g., different plane spacings d₃,d₄-d₅, d₆ of the respective crystal lattice planes), and therefore takesa value different from half value width v₂ of the diffraction peak atthe X-ray penetration depth of 5 μm.

Referring to FIG. 4( b), half value width v₁ of the diffraction peak atthe X-ray penetration depth of 0.3 μm and half value width v₂ of thediffraction peak at the X-ray penetration depth of 5 μm appear on thediffraction profile relating to the arbitrary specific parallel crystallattice planes of the crystal in the above case. Therefore, theirregular distortion of the crystal surface layer can be expressed bythe value of |v₁−v₂| which is a difference between v₁ and v₂.

In the nitride crystal of this embodiment, the irregular distortion atthe surface layer represented by the value of |v₁−v₂| is equal to orlower than 150 arcsec. Owing to the fact that the irregular distortionat the surface layer of the nitride crystal satisfies the relationshipof |v₁−v₂|≦150 (arcsec), a semiconductor layer of good crystallinity canbe epitaxially grown on the nitride crystal, and a semiconductor deviceof good characteristics can be produced.

Third Embodiment

A nitride crystal of this embodiment is characterized in that, on arocking curve measured by varying an X-ray penetration depth from acrystal surface in connection with X-ray diffraction of arbitraryspecific parallel crystal lattice planes of the crystal, a planeorientation deviation of the specific parallel crystal lattice planesrepresented by a value of |w₁−w₂| obtained from a half value width w₁ ofa diffraction intensity peak at the X-ray penetration depth of 0.3 μmand a half value width w₂ of the diffraction intensity peak at the X-raypenetration depth of 5 μm is equal to or lower than 400 arcsec.

Referring to FIG. 1, the X-ray penetration depth of 0.3 μm correspondsto a distance from the surface of the nitride crystal to an inside ofcrystal surface layer 1 a, and the X-ray penetration depth of 5 μmcorresponds to a distance from the surface of the nitride crystal to aninside of crystal inner layer 1 c. Referring to FIG. 5( a), half valuewidth w₂ at the X-ray penetration depth of 5 μm can be considered as thehalf value width of the crystal in the original state, but half valuewidth w₁ at the X-ray penetration depth of 0.3 μm reflects the planeorientation deviation of the crystal lattice at the crystal surfacelayer due to an influence of surface working of the crystal (e.g.,different plane orientation of respective specific parallel crystallattice planes 51 d, 52 d and 53 d of each crystal region), andtherefore takes a value different from half value width w₂ at the X-raypenetration depth of 5 μm.

Referring to FIG. 5( b), half value width w₁ at the X-ray penetrationdepth of 0.3 μm and half value width w₂ at the X-ray penetration depthof 5 μm appear on the rocking curve relating to the arbitrary specificparallel crystal lattice planes of the crystal in the above case.Therefore, the plane direction deviation of the specific parallelcrystal lattice planes of the crystal surface layer can be expressed bythe value of |w₁−w₂| which is a difference between w₁ and w₂.

In the nitride crystal of this embodiment, the plane orientationdeviation of the specific parallel crystal lattice planes of the surfacelayer represented by the value of |w₁−w₂| is equal to or lower than 400arcsec. Owing to the fact that the plane orientation deviation of thespecific parallel crystal lattice planes of the surface layer of thenitride crystal satisfies the relationship of |w₂−w₂|≦400 (arcsec), asemiconductor layer of good crystallinity can be epitaxially grown onthe nitride crystal, and a semiconductor device of good characteristicscan be produced.

The crystallinity evaluated by the crystallinity evaluating methods ofthe first to third embodiments described above is not restricted to thataffected by the surface working already described, and may include adistortion of the crystal and the like that occur when the crystalgrows.

In the nitride crystals of the first to third embodiments alreadydescribed, the surface of the crystal preferably has a surface roughnessRy of 30 nm or lower. Surface roughness Ry is a sum of a height from anaverage plane of a sampling portion to the highest peak thereof and adepth from the average plane to the lowest bottom, and this samplingportion is extracted from a roughness curved plane as a reference areameasuring 10 μm per side (i.e., 10 μm×10 μm=100 μm²) in a direction ofits average plane. Owing to the fact that the nitride crystal hassurface roughness Ry of 30 nm or lower, the semiconductor layer of goodcrystallinity can be epitaxially grown on the nitride crystal, and thesemiconductor device of good characteristics can be produced.

In the nitride crystals of the first to third embodiments alreadydescribed, the surface of the crystal preferably has a surface roughnessRa of 3 nm or lower. Surface roughness Ra is a value obtained byaveraging, with a reference area, a sum of absolute values of deviationsfrom an average plane of a sampling portion to a measurement curvedsurface, and this sampling portion is extracted from a roughness curvedplane as a reference area measuring 10 μm per side in a direction of theaverage plane. Owing to the fact that the nitride crystal has surfaceroughness Ra of 3 nm or lower, the semiconductor layer of goodcrystallinity can be epitaxially grown on the nitride crystal, and thesemiconductor device of good characteristics can be produced.

In the nitride crystals of the first to third embodiments alreadydescribed, it is preferable that the surface of the crystal is parallelto a C-plane in a wurtzite structure. The C-plane represents {0001}plane and {000-1} plane. The surface of group nitride crystal isparallel to each of the above planes in the wurtzite structure or isnearly parallel (e.g., at an off angle lower than 0.05° between thesurface of the nitride crystal and the C-plane in the wurtzitestructure), whereby the semiconductor layer of good crystallinity can beepitaxially grown on the nitride crystal, and the semiconductor deviceof good characteristics can be produced.

In the nitride crystals of the first to third embodiments alreadydescribed, it is preferable that the surface of the crystal forms an offangle in a range from 0.05° to 15° with respect to the C-plane in thewurtzite structure. Provision of the off angle of 0.05° or more canreduce defects at the semiconductor layer that is epitaxially grown onthe nitride crystal. However, when the off angle exceeds 15°, a step ora difference in level is liable to occur. From the viewpoint of this,the preferable off angle is from 0.1° to 10°.

Fourth Embodiment

This embodiment is a nitride crystal substrate formed of the nitridecrystal of the first to third embodiments already described. One or moresemiconductor layer(s) are epitaxially grown on at least one of mainsurfaces of the nitride crystal substrate of the embodiment to providean epilayer-containing nitride crystal substrate including the one ormore semiconductor layer(s) that are the epitaxial layer(s) alsoreferred to as the “epilayer(s)”. In this case, the semiconductor layercan be epitaxially grown on the nitride crystal substrate when a latticeconstant k₀ of the nitride crystal substrate (i.e., the lattice constantin an axis perpendicular to a crystal growth plane (this explanation isalso true in the following description of this embodiment)) and alattice constant k of the semiconductor layer satisfy a relationship of(|k−k₀|/k)≦0.15. It is preferable to satisfy a relationship of(|k−k₀|/k)≦0.05. From the viewpoint of this, the semiconductor layer ispreferable a III group nitride layer.

Fifth Embodiment

This embodiment is a semiconductor device including one or moresemiconductor layer(s) formed by epitaxial growth on at least one ofmain surface sides of the nitride crystal substrate of the above fourthembodiment or the above epilayer-containing nitride crystal substrate.In the semiconductor device thus obtained, since at least one of theuniform distortion, the irregular distortion and the plane orientationdeviation of the surface layer of the nitride crystal used as thesubstrate is small, the semiconductor layer formed on at least one ofthe main surfaces of the nitride crystal substrate or theepilayer-containing nitride crystal substrate has good crystallinity,and good device characteristics can be obtained.

The foregoing matters related to the semiconductor layer of the fourthembodiment can also be applied to the semiconductor layer of thisembodiment. More specifically, the semiconductor layer can beepitaxially grown on the nitride crystal substrate when lattice constantk₀ of the nitride crystal substrate (i.e., the lattice constant in anaxis perpendicular to the crystal growth plane (this explanation is alsotrue in the following description of this embodiment)) and latticeconstant k of the semiconductor layer satisfy the relationship of(|k−k₀|/k)≦0.15. It is preferable to satisfy the relationship of(|k−k₀|/k)≦0.05. From the viewpoint of this, the semiconductor layer ispreferable the III group nitride layer.

The semiconductor device of this embodiment may be a light-emittingelement such as a light-emitting diode or a laser diode, an electronicelement such as a rectifier, a bipolar transistor, a field-effecttransistor or a HEMT (High Electron Mobility Transistor), asemiconductor sensor such as a temperature sensor, a pressure sensor, aradiation sensor or a visible-ultraviolet ray detector, or a SAW device(Surface Acoustic Wave device).

Sixth Embodiment

Referring to FIG. 6, a semiconductor device of this embodiment is asemiconductor device including the foregoing nitride crystal substrateor the epilayer-containing nitride crystal substrate as a substrate 610,and includes a light emitting element including a plurality of (i.e.,three or more) semiconductor layers 650 formed by the epitaxial growthon one of the main surface sides of the nitride crystal substrate or theepilayer-containing nitride crystal substrate (substrate 610), a firstelectrode 661 formed on the other main surface side of the nitridecrystal substrate or the epilayer-containing nitride crystal substrate(substrate 610), and a second electrode 662 formed on the outermostsemiconductor layer of the plurality of semiconductor layers 650. Thesemiconductor device further includes a conductor 682 bearing the lightemitting element. A side of the light emitting element defined bysubstrate 610 is a light emitting side, and a side defined by theoutermost semiconductor layer side is a mount side. The plurality ofsemiconductor layers 650 include a p-type semiconductor layer 630, ann-type semiconductor layer 620 and a light emitting layer 640 formedbetween these conductive semiconductor layers. Owing to the abovestructure, it is possible to form the semiconductor device of whichnitride crystal substrate side is the light emitting side.

The semiconductor device of this embodiment has a good property ofreleasing heat generated by a light emitting layer as compared with asemiconductor device of which semiconductor layer side is the lightemitting side. Therefore, even in the operation with a high power,temperature rising of the semiconductor device is suppressed, and lightemission at high brightness can be achieved. An insulating substratesuch as a sapphire substrate must have a single-side electrode structurein which two kinds of electrodes, i.e., n- and p-electrodes are formedon the semiconductor layer. However, the semiconductor device of thisembodiment can have a double-sided electrode structure in which theelectrodes are formed on the semiconductor layer and the substrate,respectively, and a major portion of the main surface of thesemiconductor device can be used as a light emitting surface. Further,when mounting the semiconductor device, the manufacturing process can besimple, e.g., because wire boding is required only one time. Thisadvantage and the like can also be achieved.

Seventh Embodiment

This embodiment is a method of manufacturing a semiconductor deviceincluding a nitride crystal substrate or an epilayer-containing nitridecrystal substrate including one or more semiconductor layer(s) formed byepitaxial growth on at least one of main surface sides of the nitridecrystal substrate. This method of manufacturing the semiconductor deviceincludes the steps of selecting the nitride crystal of the firstembodiment as the nitride crystal substrate, and epitaxially growing theone or more semiconductor layer(s) on at least one of the main surfacesides of the substrate.

Since the nitride crystal of the first embodiment selected as thenitride crystal substrate of the semiconductor device of the seventhembodiment has the surface layer of which uniform distortion is small,the semiconductor layer of good crystallinity can be epitaxially grownon the nitride crystal, and the semiconductor device of goodcharacteristics can be formed. The foregoing matters related to thesemiconductor layers of the fourth and fifth embodiments can be appliedto the semiconductor layer of the seventh embodiment.

Eighth Embodiment

This embodiment is a method of manufacturing a semiconductor deviceincluding a nitride crystal substrate or an epilayer-containing nitridecrystal substrate including one or more semiconductor layer(s) formed byepitaxial growth on at least one of main surface sides of the nitridecrystal substrate. This method of manufacturing the semiconductor deviceincludes the steps of selecting the nitride crystal of the secondembodiment as the nitride crystal substrate, and epitaxially growing oneor more semiconductor layer(s) on at least one of main surface sides ofthe substrate.

Since the nitride crystal of the second embodiment selected as thenitride crystal substrate of the semiconductor device of the eighthembodiment has the surface layer of which irregular distortion is small,the semiconductor layer of good crystallinity can be epitaxially grownon the nitride crystal, and the semiconductor device of goodcharacteristics can be formed. The foregoing matters related to thesemiconductor layers of the fourth and fifth embodiments can be appliedto the semiconductor layer of the eighth embodiment.

Ninth Embodiment

This embodiment is a method of manufacturing a semiconductor deviceincluding a nitride crystal substrate or an epilayer-containing nitridecrystal substrate including one or more semiconductor layer(s) formed byepitaxial growth on at least one of main surface sides of the nitridecrystal substrate. This method of manufacturing the semiconductor deviceincludes the steps of selecting the nitride crystal of the thirdembodiment as the nitride crystal substrate, and epitaxially growing oneor more semiconductor layer(s) on at least one of main surface sides ofthe substrate.

Since the nitride crystal of the third embodiment selected as thenitride crystal substrate of the semiconductor device of the ninthembodiment includes the surface layer having specific parallel crystallattice planes of which plane orientation deviation is small, thesemiconductor layer of good crystallinity can be epitaxially grown onthe nitride crystal, and the semiconductor device of goodcharacteristics can be formed. The foregoing matters related to thesemiconductor layers of the fourth and fifth embodiments can be appliedto the semiconductor layer of the ninth embodiment.

The nitride crystal can be grown by a vapor phase growth method such asa HVPE (Hydride Vapor Phase Epitaxy) method or a sublimation method, ora liquid phase growth method such as a flux method.

A nitride crystal that will form the nitride crystal substrate of thesemiconductor device is cut from the nitride crystal obtained by theforegoing growth method, and surface working such as grinding andpolishing is performed for smoothing the surfaces thereof. In themechanical working such as grinding and mechanical polishing included inthe above surface working, hard grains cut into the crystal to removethe material so that work-affected layer (damaged layer) havingdeteriorated crystallinity is left at the surface of the nitride crystalthat will form the nitride crystal substrate. Therefore, thework-affected layer must be reduced for producing the III group nitridesemiconductor layer on the substrate smoothed by the mechanical working.The CMP processing is most suitable for reducing the work-affected layerbecause it can reduce both the work-affected layer and the surfaceroughness.

It is not necessary to remove completely the work-affected layer at thesubstrate surface, and the surface quality can be improved by annealingprocessing before the epitaxial growth. The annealing before the growthcauses rearrangement at the crystal surfaces, and allows the epitaxialgrowth of the semiconductor layer of good crystallinity.

As a preferred example of the surface processing method for improvingthe crystallinity of the surface layer of the nitride crystal, the CMPsurface treatment method will now be described. It is preferable that avalue x of pH and a value y (mV) of an oxidation-reduction potential ina slurry solution used in the CMP satisfy both the following equations(2) and (3):

y≧−50x+1000  (2)

y≦−50x+1900  (3)

In the case of y<−50x+1000, a polishing speed becomes low. In the caseof y>−50×+1900, a polishing pad and a polishing device are subjected toa large corrosion effect so that stable polishing becomes difficult.

From the viewpoint of further improving the polishing speed, it isfurther preferable to satisfy additionally the following equation (4):

y≧−50x+1300  (4)

The slurry of the CMP usually contains an acid such as hydrochloricacid, sulfuric acid or nitric acid, and/or an alkali such as KOH or NaOHthat are added thereto. However, the effect of oxidizing the surface ofthe chemically stable gallium nitride is small when such acid and/oralkali are used alone. Accordingly, it is preferable to increase theoxidation-reduction potential by adding an oxidizer so that therelationships of the foregoing equations (2) and (3), or the foregoingequations (3) and (4) may be satisfied.

The oxidizer added to the slurry of the CMP is not particularlyrestricted, but is preferably selected from among chlorinatedisocyanuric acids such as trichloroisocyanuric acid, chlorinatedisocyanurates such as sodium dichloroisocyanurate, permanganates such aspotassium permanganate, dichromates such as potassium dichromate,bromates such as potassium bromate, thiosulfates such as sodiumthiosulfate, hypochlorous acid, nitrates, hydrogen peroxide solutionsand ozone. Each of these oxidizers may be used alone, or two or more ofthem may be used in combination.

It is preferable that the pH of slurry of the CMP is 6 or lower, or 8 ormore. Acidic slurry having a pH of 6 or lower, or basic slurry having apH of 8 or more is brought into contact with the III group nitridecrystal to etch and remove the work-affected layer of the III groupnitride crystal so that the polishing speed can be increased. From theviewpoint of this, it is more preferable that the pH of slurry is 4 orlower, or 10 or higher.

The acid and base used for controlling the pH of slurry are notparticularly restricted, and may be selected, e.g., from among inorganicacids such as hydrochloric acid, nitric acid, sulfuric acid andphosphoric acid, organic acids such as formic acid, acetic acid, citricacid, malic acid, tartaric acid, succinic acid, phthalic acid andfumaric acid, bases such as KOH, NaOH and NH₄OH and amine, and saltssuch as sulfate, carbonate and phosphate. Also, the pH can be controlledby addition of the above oxidizer.

The slurry of the CMP preferably contains grains. These grains canincrease the polishing speed. The grains contained in the slurry are notparticularly restricted, and may be hard grains having a higher hardnessthan the nitride crystal, soft grains having a lower hardness than thenitride crystal, or grain mixtures of the hard and soft grains.

COMPARATIVE EXAMPLE 1

An n-type AlN crystal of 500 μm in thickness that was grown by the HVPEmethod and was doped with Si was used as the nitride crystal, and wasmechanically polished as follows. A Ga-side C-plane ((0001) plane) ofthe n-type GaN crystal having a diameter of 50 mm and a thickness of 500μm was pressed against a surface table of a lapping apparatus whilesupplying slurry containing diamond grains in a dispersed fashion ontothe surface table, and thereby the n-type GaN crystal was mechanicallypolished. The surface table was a copper or tin surface table. Threekinds of grains having different diameters of 6 μm, 3 μm and 1 μm,respectively, were prepared, and the grain diameters of the grains to beused were lowered stepwise in accordance with progress of the mechanicalpolishing. However, the polishing pressure in the mechanical polishingwas from 100 gf/cm² to 500 gf/cm², and a rotation speed of the surfacetable was from 30 rpm to 100 rpm.

Then, measuring processing was effected on the n-type GaN crystalsubjected to the mechanical polishing to measure diffraction X-rays from(10-13) planes of the wurtzite structure while changing the X-raypenetration depth from 0.3 μm to 5 μm, and thereby to obtain a planespacing of the (10-13) planes (the specific parallel crystal latticeplanes in this measurement) and a half value width of a diffractionintensity peak on a diffraction profile as well as a half value width ofa diffraction intensity peak on a rocking curve. A parallel opticalsystem and an X-ray wavelength of CuK_(α1) were used for the X-raydiffraction measurement. The X-ray penetration depth was controlled bychanging at least one of X-ray incident angle ω to the crystal surface,inclination angle X of the crystal surface and rotary angle of φ withinthe crystal surface. Surface roughness Ry and surface roughness Ra ofthis n-type GaN crystal were measured with an AFM (Atomic ForceMicroscope: DIMENSION N3100 manufactured by VEECO Corp). The result isrepresented in a table 1.

Referring to FIG. 6, an n-type GaN layer 621 (dopant: Si) of 1 μm inthickness forming n-type semiconductor layer 620, an n-typeAl0.1Ga_(0.9)N layer 622 (dopant: Si) of 150 nm in thickness alsoforming n-type semiconductor layer 620, light emitting layer 640, ap-type Al_(0.2)Ga_(0.8)N layer 631 (dopant: Mg) of 20 nm in thicknessforming p-type semiconductor layer 630 and a p-type GaN layer 632(dopant: Mg) of 150 nm in thickness also forming p-type semiconductorlayer 630 were successively formed by a MOCVD method on one of the mainsurface sides of substrate 610 of the n-type GaN crystal, therebyobtaining epitaxially-grown-layers for a light emitting element. Lightemitting layer 640 had a multiple quantum-well structure in which fourbarrier layers formed of GaN layers each having a thickness of 10 nm andthree well layers formed of Ga_(0.85)In_(0.15)N layers each having athickness of 3 nm were layered alternately.

A layered structure formed of a Ti layer of 200 nm in thickness, an Allayer of 1000 nm in thickness, a Ti layer of 200 nm in thickness and anAu layer of 2000 nm in thickness is formed as first electrode 661 on theother main surface side of substrate 610 of the n-type GaN crystal, andwas heated in a nitrogen atmosphere to form an n-side electrode of 100μm in diameter. Also, a layered structure formed of an Ni layer of 4 nmin thickness and an Au layer of 4 nm in thickness was formed as secondelectrode 662 on p-type GaN layer 632, and was heated in an inert gasatmosphere to form a p-side electrode. A chip measuring 400 μm per sidewas prepared from the above layered structure, and then the above p-sideelectrode was bonded to conductor 682 with a solder layer 670 made ofAuSn. Further, the n-side electrode and a conductor 681 were bondedtogether with a wire 690 so that a semiconductor device 600 having astructure as the light emitting device was obtained. The semiconductordevice thus obtained was arranged in an integrating sphere. Then, acurrent of 20 mA is supplied to the semiconductor device to emit light,and the output of light gathered by the integrating sphere was measured.However, light emission from the semiconductor device of thiscomparative example was not confirmed. The result is represented in thetable 1.

EXAMPLES 1-7

Semiconductor devices were produced under the same conditions as thoseof the comparative example 1 except for that CMP was performed under theconditions described in the table 1 after the mechanical polishing andbefore the X-ray diffraction. Light outputs of the producedsemiconductor devices were measured similarly to the comparativeexample 1. The result is represented in the table 1.

TABLE 1 COMPARATIVE EXAMPLE 1 EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 CMP pH OFSLURRY NO CMP 9.5 2.4 3.5 OXIDATION-REDUCTION 980 1420 1200 POTENTIAL OFSLURRY (mV) OXIDIZER Na-DCIA TCIA TCIA HARD GRAIN — — Al₂O₃ GRAINDIAMETER (μm) — — 0.5 SOFT GRAIN SiO₂ SiO₂ — MIXTURE VOLUME — — — RATIO((HARD GRAINS): (SOFT GRAINS)) POLISHING RATE (μm/hr) 0.4 0.5 1.1CHARACTERISTICS | d₁ − d₂ |/d₂ 2.3 × 10⁻³ 0.3 × 10⁻³ 0.3 × 10⁻³ 1.0 ×10⁻³ | v₁ − v₂ | (arcsec) 290 60 50 90 | w₁ − w₂ | (arcsec) 500 130 120220 SURFACE ROUGHNESS >100 1.8 1.0 4.1 Ry (nm) SURFACE ROUGHNESS >100.15 0.09 0.42 Ra (nm) LIGHT OUTPUT (mW) — 15.6 16.4 12.3 EXAMPLE 4EXAMPLE 5 EXAMPLE 6 EXAMPLE 7 CMP pH OF SLURRY 3.5 3.5 3.5 3.0OXIDATION-REDUCTION 1200 1200 1200 1200 POTENTIAL OF SLURRY (mV)OXIDIZER TCIA TCIA TCIA TCIA HARD GRAIN Al₂O₃ Al₂O₃ Al₂O₃ Cr₂O₃ GRAINDIAMETER (μm) 1.0 2.0 0.5 0.8 SOFT GRAIN — — SiO₂ SiO₂ MIXTURE VOLUME —— 10:90 10:90 RATIO ((HARD GRAINS): (SOFT GRAINS)) POLISHING RATE(μm/hr) 1.6 1.9 0.8 1.5 CHARACTERISTICS | d₁ − d₂ |/d₂ 1.7 × 10⁻³ 2.1 ×10⁻³ 0.6 × 10⁻³ 1.4 × 10⁻³ | v₁ − v₂ | (arcsec) 130 150 80 110 | w₁ − w₂| (arcsec) 340 400 190 300 SURFACE ROUGHNESS 5.3 8.9 2.9 4.8 Ry (nm)SURFACE ROUGHNESS 0.51 0.85 0.26 0.45 Ra (nm) LIGHT OUTPUT (mW) 9.8 8.213.9 10.7 (NOTE) NA-DCIA: SODIUM DICHLOROISOCYANURATE, TCIA:TRICHLOROISOCYANURIC ACID

COMPARATIVE EXAMPLE 2

An n-type AlN crystal of 400 μm in thickness that was grown by thesublimation method and was doped with Si was used as the nitridecrystal, and was mechanically polished similarly to the comparativeexample 1.

Then, measuring processing was effected on the n-type AlN crystalsubjected to the mechanical polishing to measure diffraction X-rays from(11-22) planes of the wurtzite structure while changing the X-raypenetration depth from 0.3 μm to 5 μm, and thereby to obtain a placespacing of the (11-22) planes (specific parallel crystal lattice planesin this measurement) and a half value width of a diffraction intensitypeak on a diffraction profile as well as a half value width of thediffraction intensity peak on a rocking curve. A parallel optical systemand an X-ray wavelength of CuK_(α1) were used for the X-ray diffractionmeasurement. The X-ray penetration depth was controlled by changing atleast one of X-ray incident angle ω to the crystal surface, inclinationangle X of the crystal surface and rotary angle of φ within the crystalsurface. Surface roughness Ry and surface roughness Ra of this n-typeAlN crystal were measured with the AFM. The result is represented in atable 2.

A semiconductor device using the above AlN crystal as a substrate wasproduced similarly to the comparative example 1. A light output of thesemiconductor device thus produced was measured similarly to thecomparative example 1. Light emission was not confirmed. The result isrepresented in the table 2.

EXAMPLES 8-10

Semiconductor devices were produced under the same conditions as thoseof the comparative example 2 except for that CMP was performed under theconditions described in the table 2 after the mechanical polishing andbefore the X-ray diffraction. The result is represented in the table 2.

TABLE 2 COMPARATIVE EXAMPLE 2 EXAMPLE 8 EXAMPLE 9 EXAMPLE 10 CMP pH OFSLURRY NO CMP 9.5 2.4 3.5 OXIDATION-REDUCTION 980 1420 1200 POTENTIAL OFSLURRY (mV) OXIDIZER Na-DCIA TCIA TCIA HARD GRAIN — — Al₂O₃ GRAINDIAMETER — — 0.5 (μm) SOFT GRAIN SiO₂ SiO₂ — MIXTURE VOLUME — — — RATIO((HARD GRAINS):(SOFT GRAINS)) POLISHING RATE 0.6 0.8 1.4 (μm/hr)CHARACTERISTICS | d₁ − d₂ |/d₂ 2.4 × 10⁻³ 0.5 × 10⁻³ 0.4 × 10⁻³ 1.4 ×10⁻³ | v₁ − v₂ | (arcsec) 310 80 70 110 | w₁ − w₂ | (arcsec) 510 140 130220 SURFACE >100 1.0 1.4 4.5 ROUGHNESS Ry (nm) SURFACE >10 0.09 0.120.41 ROUGHNESS Ra (nm) LIGHT OUTPUT — 13.9 14.8 10.9 (mW) (NOTE)NA-DCIA: SODIUM DICHLOROISOCYANURATE TCIA: TRICHLOROISOCYANURIC ACID

As is apparent from the foregoing tables 1 and 2, high light outputswere achieved by the LEDs that are the semiconductor devices eachselectively employing, as the nitride crystal substrate, the nitridecrystal satisfying the conditions that, in the X-ray diffractionmeasurement performed with variation of X-ray penetration depth from thecrystal surface while X-ray diffraction conditions of the arbitraryspecific parallel crystal lattice planes of the crystal are satisfied,the uniform distortion |d₁−d₂|/d₂ at the surface layer obtained from theplane spacing d₁ of the specific parallel crystal lattice planes at theX-ray penetration depth of 0.3 μm and the plane spacing d₂ of thespecific parallel crystal lattice planes at the X-ray penetration depthof 5 μm is equal to or lower than 2.1×10⁻³, the irregular distortion|v₁−v₂| at the crystal surface layer obtained from the half value widthv₁ of the diffraction intensity peak at the X-ray penetration depth of0.3 μm and the half value width v₂ of the diffraction intensity peak atthe X-ray penetration depth of 5 μm is equal to or lower than 150arcsec, or the plane direction deviation |w₁−w₂| of the specificparallel crystal lattice plane obtained from the half value width w₁ ofthe diffraction intensity peak at the X-ray penetration depth of 0.3 μmand the half value width w₂ of the diffraction intensity peak at theX-ray penetration depth of 5 μm is equal to or lower than 400 arcsec.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A nitride crystal, wherein, in connection with plane spacing ofarbitrary specific parallel crystal lattice planes of the nitridecrystal obtained from X-ray diffraction measurement performed withvariation of X-ray penetration depth from a surface of said crystalwhile X-ray diffraction conditions of said specific parallel crystallattice planes being satisfied, a uniform distortion at a surface layerof said crystal represented by a value of |d₁−d₂|/d₂ obtained from saidplane spacing d₁ at said X-ray penetration depth of 0.3 μm and saidplane spacing d₂ at the X-ray penetration depth of 5 μm is equal to orlower than 2.1×10⁻³.
 2. A nitride crystal, wherein, on a diffractionintensity profile of arbitrary specific parallel crystal lattice planesof the nitride crystal obtained from X-ray diffraction measurementperformed with variation of X-ray penetration depth from a surface ofsaid crystal while X-ray diffraction conditions of said specificparallel crystal lattice planes being satisfied, an irregular distortionat a surface layer of said crystal represented by a value of |v₁−v₂|obtained from a half value width v₁ of a diffraction intensity peak atsaid X-ray penetration depth of 0.3 μm and a half value width v₂ of thediffraction intensity peak at said X-ray penetration depth of 5 μm isequal to or lower than 150 arcsec.
 3. A nitride crystal, wherein, on arocking curve measured by varying an X-ray penetration depth from asurface of the nitride crystal in connection with X-ray diffraction ofarbitrary specific parallel crystal lattice planes of said crystal, aplane orientation deviation of said specific parallel crystal latticeplanes represented by a value of |w₁−w₂| obtained from a half valuewidth w₁ of a diffraction intensity peak at said X-ray penetration depthof 0.3 μm and a half value width w₂ of the diffraction intensity peak atsaid X-ray penetration depth of 5 μm is equal to or lower than 400arcsec.
 4. The nitride crystal according to claim 1, wherein saidsurface of said crystal has a surface roughness Ry of 30 nm or lower. 5.The nitride crystal according to claim 1, wherein said surface of saidcrystal has a surface roughness Ra of 3 nm or lower.
 6. The nitridecrystal according to claim 1, wherein said surface of said nitridecrystal is parallel to a C-plane of a wurtzite structure.
 7. The nitridecrystal according to claim 1, wherein said surface of said nitridecrystal has an off angle in a range from 0.05° to 15° with respect to aC-plane of a wurtzite structure.
 8. A nitride crystal substrate formedof the nitride crystal according to claim
 1. 9. An epilayer-containingnitride crystal substrate comprising: one or more semiconductor layer(s)formed by epitaxial growth on at least one of main surface sides of thenitride crystal substrate according to claim
 8. 10-14. (canceled)
 15. Asemiconductor device comprising, a nitride crystal substrate, or anepilayer-containing nitride crystal substrate including one or moresemiconductor layer(s) formed by epitaxial growth on at least one ofmain surface sides of said nitride crystal substrate, and one or moresemiconductor layer(s) formed by epitaxial growth on at least one of themain surface sides of said nitride crystal substrate or saidepilayer-containing nitride crystal substrate, wherein on a diffractionintensity profile of arbitrary specific parallel crystal lattice planesof the nitride crystal obtained from X-ray diffraction measurementperformed with variation of X-ray penetration depth from a surface ofsaid crystal while X-ray diffraction conditions of said specificparallel crystal lattice planes being satisfied, an irregular distortionat a surface layer of said crystal represented by a value of |v₁−v₂|obtained from a half value width v₁ of a diffraction intensity peak atsaid X-ray penetration depth of 0.3 μm and a half value width v₂ of thediffraction intensity peak at said X-ray penetration depth of 5 μm isequal to or lower than 150 arcsec.
 16. A semiconductor devicecomprising, a nitride crystal substrate or an epilayer-containingnitride crystal substrate including one or more semiconductor layer(s)formed by epitaxial growth on at least one of main surface sides of saidnitride crystal substrate, a light-emitting element including three ormore semiconductor layers formed by epitaxial growth on one of the mainsurface sides of said nitride crystal substrate or saidepilayer-containing nitride crystal substrate, a first electrode formedon the other main surface side of said nitride crystal substrate or saidepilayer-containing nitride crystal substrate, a second electrode formedon the outermost semiconductor layer among said plurality ofsemiconductor layers, a conductor bearing said light-emitting element;and a substrate side of said light emitting element is a light emittingside, an outermost semiconductor layer side is a mount side, and saidplurality of semiconductor layers include a p-type semiconductor layer,an n-type semiconductor layer and a light emitting layer formed betweenthese conductive semiconductor layers, wherein on a diffractionintensity profile of arbitrary specific parallel crystal lattice planesof the nitride crystal obtained from X-ray diffraction measurementperformed with variation of X-ray penetration depth from a surface ofsaid crystal while X-ray diffraction conditions of said specificparallel crystal lattice planes being satisfied, an irregular distortionat a surface layer of said crystal represented by a value of |v₁−v₂|obtained from a half value width v₁ of a diffraction intensity peak atsaid X-ray penetration depth of 0.3 μm and a half value width v₂ of thediffraction intensity peak at said X-ray penetration depth of 5 μm isequal to or lower than 150 arcsec.
 17. A semiconductor devicecomprising, a nitride crystal substrate, or an epilayer-containingnitride crystal substrate including one or more semiconductor layer(s)formed by epitaxial growth on at least one of main surface sides of saidnitride crystal substrate, and one or more semiconductor layer(s) formedby epitaxial growth on at least one of the main surface sides of saidnitride crystal substrate or said epilayer-containing nitride crystalsubstrate, wherein on a rocking curve measured by varying an X-raypenetration depth from a surface of the nitride crystal in connectionwith X-ray diffraction of arbitrary specific parallel crystal latticeplanes of said crystal, a plane orientation deviation of said specificparallel crystal lattice planes represented by a value of |w₁−w₂|obtained from a half value width w₁ of a diffraction intensity peak atsaid X-ray penetration depth of 0.3 μm and a half value width w₂ of thediffraction intensity peak at said X-ray penetration depth of 5 μm isequal to or lower than 400 arcsec.
 18. A semiconductor devicecomprising, a nitride crystal substrate or a epilayer-containing nitridecrystal substrate including one or more semiconductor layer(s) formed byepitaxial growth on at least one of main surface sides of said nitridecrystal substrate, a light-emitting element including three or moresemiconductor layers formed by epitaxial growth on one of the mainsurface sides of said nitride crystal substrate or saidepilayer-containing nitride crystal substrate, a first electrode formedon the other main surface side of said nitride crystal substrate or saidepilayer-containing nitride crystal substrate, a second electrode formedon the outermost semiconductor layer among said plurality ofsemiconductor layers, a conductor bearing said light-emitting element;and on a rocking curve measured by varying an X-ray penetration depthfrom a surface of the nitride crystal in connection with X-raydiffraction of arbitrary specific parallel crystal lattice planes ofsaid crystal, a plane orientation deviation of said specific parallelcrystal lattice planes represented by a value of |w₁−w₂| obtained from ahalf value width w₁ of a diffraction intensity peak at said X-raypenetration depth of 0.3 μm and a half value width w₂ of the diffractionintensity peak at said X-ray penetration depth of 5 μm is equal to orlower than 400 arcsec.